Various nonspecific serum antibody tests for the diagnosis of feline infectious peritonitis virus (FIPV) are known. These known procedures include the testing of cat sera for immunofluorescent staining of coronavirus infected cell lines. Many of these assays rely upon the antigenic relationship which exists between FIPV and other coronaviruses and utilize either transmissible gastroenteritis virus (TGEV) of swine, canine coronavirus or human respiratory coronavirus. These assays accordingly provide only nonspecific detection of antibody to coronavirus common antigenic determinants. In particular, because of the substantial antigenic similarity between FIPV and feline enteric coronavirus (FeCV), such assays cannot distinguish antibody to FIPV from FeCV.